The present invention relates to a multi-channel, multi-stage network in which information is transmitted or exchanged with satisfactory efficiency, and more particularly to a method of configuration of a network which has the same connectivity between stages and has a physical topology of a star form.
In a single-channel LAN such as Ethernet, Token ring being popularized at the present time, a channel is shared among NIU's (network interface units). Therefore, the throughput per NIU is lowered in inverse proportion to the increase in number of NIU's. To improve the throughput, it is effective to provide a plurality of channels but the routing is required since nodes lie scattered at different channels. A shufflenet, which is one configuration of a multi-channel network, has been proposed as a network in which the lowering of the throughput in the single-channel network is suppressed and an effective routing is made. The shufflenet is disclosed by AT&T Technical Journal, November/December 1987, Volume 66, issue 6, pp. 21-34 and U.S. Pat. No. 4,931,959. The former reference shows a connectivity graph which defines a shufflenet (or an inter-NIU connection diagram) and examples of the shufflenet which are realized by topologies taking the forms of bus, ring and star. The shufflenet is a multi-stage network in which a group of NIU's are handled as one stage (hereinafter referred to as column) and the columns are interconnected by a connectivity graph called a perfect shuffle. In the shufflenet, provided that the number of transmitters and receivers per NIU is p and the number of columns is k, the number of NIU's per column is p.sup.k and the NIU's in the whole of the network is k.times.p.sup.k. In this case, the total number of channels amounts to p.times.k.times.p.sup.k. FIG. 4 shows a connectivity graph disclosed by the above-mentioned reference in the case where p=2 and k=3. FIGS. 5A and 5B show the constructions which are disclosed by the reference and have physically a form of star. More particularly, FIG. 5A shows a construction, based on WDM (wavelength-division multiplexing), in which transmitters are assigned with different wavelengths and are connected by a star coupler, and FIG. 5B shows a construction in which all transmitters and receivers are connected by optical fibers in one-to-one correspondence.
However, the above prior art involves the following problem. Namely, in the (p, k) shufflenet, since the number of channels required is p.times.k.times.p.sup.k, the number of wavelengths, required when the network is formed by a wavelength multiplexing transmission path shown in FIG. 5A, amounts to p.times.k.times.p.sup.k, too. Thus, as the network scale becomes large, the number of wavelengths required is remarkably increased. Also, in the construction shown in FIG. 5B, the number of optical fibers required for connection is p.times.k.times.p.sup.k, which forms a factor to restrict the installation, maintenance and extension of the network.